I have tried Musinex. I don't like the way it doesn't dissolve. I am giving her Ensure to try to put weight on her because she is skin and bones. I attribute that to her poor diet of vegetarianism and later on years of eating next to nothing. Now that she has lived with my husband and me for, well we're in our fourth year now, she eats everything I serve her twice per day with an afternoon snack of yogurt....only good, nutritious food. She was going on her own twice a day. For a month now, she has not defecated on her own. I have been giving her the Correctol after she doesn't go for a few days and you can only imagine what a crappy nightmare it is for me that next a.m. This morning, it was so bad, I just sat and cried until i could regain my composure to clean it all up. I'm hoping I can just give her that each night and it will regulate her.
If she's a vegetarian by nature, maybe you could increase the amount of vegetables she's eating. Meat is constipating. Vegetarians are not typically unhealthy and do tend to weigh less than meat-eaters. Does her doctor think that her weight is unhealthy? Does he think she needs to put on weight? The reason I ask is because joints such as the hips and knees benefit by not having to support excess weight.
If she drinks a lot of fluids, you can increase the fiber in her diet.